linux-kernel - Re: od_set_powersave_bias: NULL pointer dereference

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Message-ID: <20130626142852.GA2326@jshin-Toonie>
Date:	Wed, 26 Jun 2013 09:28:52 -0500
From:	Jacob Shin <jacob.shin@....com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	Tim Gardner <tim.gardner@...onical.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>, <cpufreq@...r.kernel.org>,
	<linux-pm@...r.kernel.org>
Subject: Re: od_set_powersave_bias: NULL pointer dereference

On Wed, Jun 26, 2013 at 12:18:27PM +0530, Viresh Kumar wrote:
> On 25 June 2013 21:49, Jacob Shin <jacob.shin@....com> wrote:
> > Yes, so sorry about that, it looks like I failed to test with:
> 
> No problem, it happens :)
> 
> > CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE=y
> > CONFIG_CPU_FREQ_GOV_PERFORMANCE=y
> > CONFIG_CPU_FREQ_GOV_ONDEMAND=y
> > CONFIG_X86_AMD_FREQ_SENSITIVITY=m
> >
> > The following patch fixes this, Tim, could you please test ? :
> >
> > ---8<---
> >
> > From 3c727b1f775448599e67c5fb2121d79448e80c90 Mon Sep 17 00:00:00 2001
> > From: Jacob Shin <jacob.shin@....com>
> > Date: Tue, 25 Jun 2013 10:40:54 -0500
> > Subject: [PATCH 1/1] cpufreq: fix NULL pointer deference at
> >  od_set_powersave_bias()
> >
> > When initializing the default powersave_bias value, we need to first
> > make sure that this policy is running the ondemand governor.
> >
> > Reported-by: Tim Gardner <tim.gardner@...onical.com>
> > Signed-off-by: Jacob Shin <jacob.shin@....com>
> > ---
> >  drivers/cpufreq/cpufreq_ondemand.c |   17 +++++++++++++----
> >  1 file changed, 13 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
> > index 4b9bb5d..93eb5cb 100644
> > --- a/drivers/cpufreq/cpufreq_ondemand.c
> > +++ b/drivers/cpufreq/cpufreq_ondemand.c
> > @@ -47,6 +47,8 @@ static struct od_ops od_ops;
> >  static struct cpufreq_governor cpufreq_gov_ondemand;
> >  #endif
> >
> > +static unsigned int default_powersave_bias;
> > +
> >  static void ondemand_powersave_bias_init_cpu(int cpu)
> >  {
> >         struct od_cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
> > @@ -543,7 +545,7 @@ static int od_init(struct dbs_data *dbs_data)
> >
> >         tuners->sampling_down_factor = DEF_SAMPLING_DOWN_FACTOR;
> >         tuners->ignore_nice = 0;
> > -       tuners->powersave_bias = 0;
> > +       tuners->powersave_bias = default_powersave_bias;
> >         tuners->io_is_busy = should_io_be_busy();
> >
> >         dbs_data->tuners = tuners;
> > @@ -585,6 +587,7 @@ static void od_set_powersave_bias(unsigned int powersave_bias)
> >         unsigned int cpu;
> >         cpumask_t done;
> >
> > +       default_powersave_bias = powersave_bias;
> 
> Why are the above three changes required? And in case they are, then
> they must have been commited separately.
> 
> >         cpumask_clear(&done);
> >
> >         get_online_cpus();
> > @@ -593,11 +596,17 @@ static void od_set_powersave_bias(unsigned int powersave_bias)
> >                         continue;
> >
> >                 policy = per_cpu(od_cpu_dbs_info, cpu).cdbs.cur_policy;
> > -               dbs_data = policy->governor_data;
> > -               od_tuners = dbs_data->tuners;
> > -               od_tuners->powersave_bias = powersave_bias;
> > +               if (!policy)
> > +                       continue;
> 
> I am not sure if this is enough. What if we had ondemand as the
> governor initially, then we changed it to something else. Now also
> cur_policy contains a address and isn't zero.

Right, so we check below ..

> 
> >                 cpumask_or(&done, &done, policy->cpus);
> > +
> > +               if (policy->governor != &cpufreq_gov_ondemand)
> > +                       continue;

This should catch that case no ?

> > +
> > +               dbs_data = policy->governor_data;
> > +               od_tuners = dbs_data->tuners;
> > +               od_tuners->powersave_bias = default_powersave_bias;
> >         }
> >         put_online_cpus();
> >  }
> > --
> > 1.7.9.5
> >
> >
> --
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